An oil sand (i.e., a reservoir whose pore volume contains a significant level of bitumen saturation) may exist substantially in isolation, or may be underlain or overlain by hydraulically contiguous formations that have significant saturations of other fluids, such as gas or water, or both.
In one such configuration which occurs commonly in Canada's oil sands, an oil sand is overlain by a contiguous gas zone with which the oil sand is in hydraulic communication.
There are several techniques known for the recovery of bitumen from the oil sand. However, we cite some technology whose well configurations may bear some resemblance to that of the present invention, but whose processes for bitumen recovery are markedly different from that of the present invention, as follows.
U.S. Pat. No. 4,116,275 to Butler et al. relates to a method for recovering hydrocarbons from a hydrocarbon-bearing formation. A heated fluid, such as steam, is injected into the formation, such as a tar sand formation, via a suitably completed horizontal well, and subsequently, formation hydrocarbons are produced via the well.
U.S. Pat. No. 4,280,559 to Best relates to a process for in situ recovery of viscous oil from a subterranean formation. Steam is injected into the formation via a well, permitted to soak, and heated fluids including heated viscous oil are produced sufficient to create a substantial fluid mobility in the formation. Then a hydrocarbon solvent is injected into the formation and another steam injection, soak and oil production cycle is performed to recover additional quantities of oil.
U.S. Pat. No. 4,344,485 to Butler relates to a thermal method for recovering normally immobile oil from a tar sand (oil sand) deposit. Two wells horizontal wells are drilled, one for injection of heated fluid (steam) and one for production of liquids. Thermal communication is established between the wells, and the wells are operated such that the mobilized oil and steam flow without substantially mixing. Oil drains continuously by gravity to the production well where it is recovered.
Canadian Patent No. 2,096,034 to Kisman et al. is directed at recovery of bitumen. The recovery process, commonly referred to as COSH_(COSH is the acronym of Combustion Override Split-production Horizontal-well), is an in situ combustion process. The COSH process mentions the use of steam injection at the vertical injector, either to establish communication with the horizontal producer or to heat the region around the vertical injector so that ignition can occur. The horizontal producer is not engaged in steam injection. Bitumen is largely mobilized from above through in situ combustion and is passively received by the horizontal well.
U.S. Pat. No. 5,626,191 to Greaves et al. describes a well arrangement in which production wells are generally horizontal, positioned low in the reservoir, with a row of vertical air injection wells that are used to propagate a combustion front within the reservoir.
Canadian Patent Application No. 2,594,413 to Nzekwu et al., titled In situ Combustion in Gas Over Bitumen Formations, relates to recovery of gas from an overlying gas zone. In this process, air is injected into a gas zone which overlies an oil sand, in situ combustion is initiated within the gas zone, and the resulting combustion gases horizontally displace the natural gas to nearby production wells for recovery. The pressuring of the gas zone may be followed by depletion of the heavy oil zone, or the depletion of the heavy oil zone may be concurrent with pressuring within the gas zone. The heavy oil may be recovered by a process that comprises injecting a heated fluid into the heavy oil zone and producing hydrocarbons from the heavy oil zone that are mobilized under the influence of gravity by the heated fluid, such as SAGD.